Many techniques about the use of synthetic sand and clay for play or education, instead of natural sand and clay, have been introduced. Disclosed is a molding composition for handcraft in Korean Patent No. 231408, a method for manufacturing viscous sand and the use thereof in stereostatic learning in Korean Patent Publication No. 2004-361, viscous sand and a method for producing the same in U.S. Pat. No. 6,235,070, a sand material mixture and a method for producing the same in Korean Patent No. 598001, a malleable play material compound resembling loose soil in U.S. Pat. No. 5,873,933, and a functional synthetic clay capable of being naturally cured and releasing scent upon pressing in Korean Patent Publication No. 2006-11619.
A brief description of each of these references is given below. The molding composition for handcraft of Korean Patent No. 231408 is prepared by blending water, salt, flour powder, starch, stone dust, aluminum sulfate, oil, borax, magnesium chloride, sodium benzoate, titanium oxide, and dye at an appropriate ratio, followed by stirring, and heating and forming, whereby the composition has the advantage of being easily kneaded even with a small amount of water, can be prevented from freezing and putrefaction, is capable of maintaining moisture, and is nice to touch due to flour powder and starch.
Korean Patent Publication No. 2004-361 pertains to a method for manufacturing viscous sand which can repeatedly be molded and dispersed according to a degree of force applied thereto. In the method, 80 to 90% by weight of sand is heated to 75 to 90° C., fed with 0.5 to 3.5% by weight of carnauba, and mixed while the temperature is maintained until the carnauba is melted to coat the sand. Then, 8 to 12% by weight of beeswax and 1.5 to 4.5% by weight of lanolin are added to the coated sand and maintained at 55 to 70° C. so that the beeswax and lanolin are melted to coat the sand therewith, after which the sand is slowly cooled.
The viscous sand of U.S. Pat. No. 6,235,070 and the sand material mixture of Korean Patent No. 598001 are common in that they comprise sand grains and a binder. The binder forms a coating on the sand grains and is selected from the group consisting of beeswax, ceresin wax, microcrystalline wax, and a mixture of ozokerite and paraffin wax. These sand material mixtures can be used as toy materials, education materials, and materials for simulated architectural design and landscape architecture in museums and aquariums, etc.
The malleable play material compound resembling loose soil of U.S. Pat. No. 5,873,933 comprises a malleable amorphous binder and a quantity of sand. The binder comprises soluble cellulose, polyvinyl alcohol, propylene glycol, water, sodium borate, and sodium carbonate. The mixture in which the malleable binder is combined with a great quantity of sand has an unusual tactile characteristic and a granular malleable amorphous property.
In addition, the functional synthetic clay capable of being naturally cured and releasing scent upon pressing, disclosed in Korean Patent Publication No. 2006-11619, is prepared by mixing polyvinyl alcohol and ethylene vinyl acetate as base materials, polyacrylonitrile powder and heat-expandable microspheres which are hollow spheres having low density as fillers, a thickener, glycerin, a retarder, and other additives at room temperature and elevated temperatures.
However, the above-mentioned, conventional viscous sand or synthetic clay were unable to attract or draw attentions from infants and children because they are substantially similar in physical and morphological properties to preexisting sand, sand with moisture or paraffin-coated oily sand, natural clay, etc. Further, such conventional sand or clay required water for its use or allowed only limited molding activities. In addition, even in case where they could be molded, conventional sand or clay were solidified with time and thus could not be repetitively used. Except for being kept as an artwork, the solidified, molded sand or clay was discarded, causing environmental pollution. Particularly, paraffin-coated viscous sand were problematic in that the paraffin would smear on floors, hands, cloths, etc., causing significant inconvenience, made it difficult to separate bacteria and dust therefrom when bacteria and dust were stuck at the sand or clay, easily putrefied to emit odors, and gave an unpleasant sticky tactile feel.
With these problems in mind, the present applicant developed air clay, which was substantially different in tactile feel and properties from conventional viscous sand or synthetic clay and could be repetitively used even without water. The air clay was registered as Korean Patent Nos. 10-0874091 and 10-1178944. Korean Patent No. 10-0874091 discloses air clay comprising a base material such as sand dust prepared by finely grinding sand and glycerin. When pulled, the air clay is stretched with the concomitant absorption of air there into, thereby becoming loose and soft like clouds, cotton, or snow. On the other hand, when agglomerated by force, the air clay returns back to dense, rigid clay shape while the absorbed air is released. Thus, the air clay overcomes various problems and limitations the conventional viscous sand or synthetic clay has. Korean Patent No. 10-1178944 describes an improved clay composition that has various properties so that it is utilized for various purposes and is modified in surface and physical properties so that it is imparted with functionality such as antibacterial activity. This clay composition comprises porous diatomite powder (first base material) and an amphipathic, that is, a hydrophilic and lipophilic liquid material, and optionally a second base material, smaller in size than the first base material, endowing various properties.
Both the air clay and the improved clay composition, developed by the present applicant, can be repetitively molded without water and can maintain constant physical properties for a long period of time without being hardened. While the air clay and composition developed by the present applicant retains properties that cannot be found in conventional clay and synthetic clay compositions, these patented inventions do not have a shape retention potential enough to maintain a molded shape as it is for a long time or to facilitate play such as throwing with agglomerates of the clay.
Hollow spheres, which are globular particles with a vacant interior, are low in density. Generally, plastic hollow spheres composed of organic polymers are widely known. Recent active research has diversified kinds of hollow sphere materials such as ceramic hollow spheres, metal hollow spheres, etc. Among them, hollow glass spheres made of the glass ingredient silica have attracted intensive attention because of their low density and excellent flame resistance and heat insulation. They are commercially manufactured on a mass scale by, for example, 3M, Emerson, etc. Hollow glass spheres find applications as a high-strength, low-density additive in a variety of materials such as resins, structural foam, elastomers, etc. Hollow glass spheres are commercially available such as those sold by Sinosteel Maanshan New Material Technology Co., Ltd., China, in the trade name of ‘Hollow Glass Microspheres’, which is made of soda-lime borosilicate glass; by 3M, U.S.A. in the trade name of ‘Glassbubbles’; and by Potters Industries LLC, U.S.A. in the name of ‘Q-Cel®’.